The invention relates to a method for simultaneously compensating for a plurality of periodic, in particular sinusoidal, disturbances occurring during the operation of an electric steering system, wherein the electric steering system comprises a torque control element, and wherein at least one compensation signal corresponding to the disturbances that are to be compensated for is determined as a function of a signal characterizing an actuating torque of the torque control element and a signal characterizing a current torsion bar torque, using a model of the steering system.
The invention further relates to a device for simultaneously compensating for a plurality of periodic, in particular sinusoidal, disturbances occurring during the operation of an electric steering system, wherein the electric steering system comprises a torque control element, and wherein at least one compensation signal corresponding to the disturbances that are to be compensated for can be determined as a function of a signal characterizing an actuating torque of the torque control element and a signal characterizing a current torsion bar torque, using a model of the steering system.
A method and a device for detecting and compensating for torsional steering wheel vibrations in an EPS steering system are known from DE 10 2009 028 448 A1. A variable-frequency disturbance and state variable calculator is provided for the compensation of the torsional steering wheel vibrations. If the presence of a disturbance frequency is detected, the variable-frequency disturbance and state variable calculator is activated. This calculator calculates an additional motor torque, which is suitable, in terms of the amplitude, frequency and phase position thereof, for compensating for the detected dominant disturbance frequency, as a function of the previously ascertained dominant disturbance frequency, a torsion bar torque filtered through a variable-frequency bandpass filter, and optionally further measured variables. The bandpass filter is required because the model of a system to be observed, which is implemented in the disturbance and state variable calculator, cannot be determined with sufficient precision across a large frequency range.
While the known method allows sufficiently good compensation for torsional steering wheel vibrations that are caused by sinusoidal disturbance frequencies for many applications, the implementation of the method requires relatively high computing power, among other things due to the complex filtering of the input signal.
Moreover, only a single sinusoidal disturbance can be compensated for by way of the known method. However, there are also situations in which it is not sufficient to compensate for a single sinusoidal disturbance frequency. For example, first- and second-order periodic vibrations occur as a result of the brake disk geometry with what is known as cold brake judder, and fifth- to tenth-order vibration forms even occur with what is known as hot brake judder. However, simultaneous compensation of multiple periodic disturbing signals is no trivial task. Analyses have shown that an enhancement of a disturbance and state variable calculator becomes too unstable with the presence of two periodic disturbing signals, which each are appropriately filtered using a bandbass filter, due to resulting different propagation times or phases of the signals, and that compensation of the disturbing signals is no longer possible due to the creation of inadvertent interactions.
Moreover, disturbance variable calculators have the fundamental problem that modeling errors or inaccuracies in the model of the controlled system, which is an integral part of the disturbance variable calculator, are mapped in the disturbance variable that is ascertained or reconstructed by way of the disturbance variable calculator (the variable, in turn, being decisive in the creation of the compensation signal). This problem is further intensified when the disturbance to be compensated for is defined for a particular structure or for a sinusoidal signal. Without the use of a bandpass filter on the input side, all disturbances acting on the input side and the modeling errors of the controlled system would act in the form of an offset on the compensation signal ascertained by way of the disturbance variable calculator, which, in turn, would be perceived by the driver as a constant offset moment or holding moment at the steering wheel.